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• ~.~ D R~-FT <br />Mi Lutes, Rpri 1 22-23, 1992 Subject To Board Approval p~ <br />Staff said the AVR or tailings treatment system acidifies the tailings <br />and volatizes the cyanide when air is pumped through the tailings <br />slurry. Staff said the volatilized cyanide is regenerated when a <br />chemical, sodium hydroxide, is added to it, and sodium cyanide is <br />produced. <br />Staff said a collection pond is located downstream below the tailings <br />dam. Through a technique referred to as thin layer deposition, Staff <br />said the tailings are transferred from the mill to the tailings dam in <br />a pipe and deposited in the tailings area. Staff explained that the <br />slurry is deposited in thin layers. Staff said that a free water pool, <br />including water that has not percolated down through the tailings, is <br />located on top of each tailings deposit area. A drain system picks up <br />the water on the bottom of the tai 1 i ngs dam, takes i t tnrough the dam <br />and deposits it in a collection pond. Staff said the water in the <br />collection pond is then pumped back to the mill through the free water <br />pools. <br />Staff said the tailings area and facilities encompass at~out 200 acres <br />and that the operator has calculated that about 52 acre-feet of water <br />is contained in the tailings structures. <br />Staff discussed the double liner system of the tailings area. The <br />underlines is a compacted clay liner, and the primary liner is <br />synthetic. Staff said all of the water from the drain system lies on <br />top of the primary liner. Staff said the collection pond has a double <br />synthetic liner with a material in between which collects leakage from <br />the first liner and diverts it to a leak detection system. Monitoring <br />wells are located above and below the tailings pond area. <br />Staff referenced a March 30, 1992 letter (included in Exhibit A) from <br />Matt Lewis, the environmental affairs manager for the operator. Staff <br />said that in the letter, Mr. Lewis informed the Division that due to a <br />very cold winter, a lot of ice had accumulated on the ponds. After the <br />ice thawed, the operator discovered that higher than anticipated <br />concentrations of cyanide existed in the tailings and collection <br />ponds. Staff said the level of cyanide discovered was no': discussed in <br />the letter and that Mr. Lewis proposed the use of zinc ferrous sulfate <br />to detoxify the tailings. The letter also referred to problems <br />associated with the AVR or treatment system for the tailings. <br />Staff said that on March 30, 1992, the Division met with the operator's <br />representatives and was then informed of elevated levels of cyanide in <br />the free water pools in the tailings area. The concentration of <br />cyanide was 80 to 200 parts per million of total cyanide and 25 parts <br />per million of free cyanide. Staff said Mr. Lewis informed the <br />Division that the operator knew of the problem in November of 1991 and <br />that the information was reported to the Division in a 4th quarter <br />report. Staff said the Division has not been able to locate the report <br />in question. <br />Staff said that on January 9, 1992, Mr. Lewis reviewed the Division's <br />files and reported that they lacked some of the monitoring information <br />